1. Field of the Invention
The present invention relates to the devices and systems used to de-head or unhead a vessel containing a fluid, distillate, or unconsolidated debris byproduct produced from a manufacturing process, such as the several types of coke produced from a petroleum refinery process, as well as to the several methods employed for unheading a vessel utilizing such devices or systems. Specifically, the present invention relates to various unheading valves, and associated methods, namely various de-header valves that may be coupled to a coke drum, particularly at its top and/or bottom openings, wherein the valve functions to safely, effectively, and efficiently de-head or unhead the coke drum following the manufacture of coke, or other byproducts, and to facilitate the removal of coke during the decoking process.
2. Background
In the hydrocarbon processing industry, many refineries recover valuable products from the heavy residual oil that remains after refining operations are completed. This recovery process is known as delayed coking and produces valuable distillates and coke in large vessels or coke drums. Coke drums are usually in operation in pairs so that when one coke drum is finished being filled with the byproduct or residual material via a feed, the feed may be directed to an empty drum so that the filled drum may be cooled and the byproduct purged from the coke drum. The process of purging coke from a coke drum in known as decoking. This allows the refinery process to operate in a cyclical, continuous manner, without undue interruption.
As stated, when one coke drum is full, it must be purged of the byproduct it holds in preparation for refilling the coke drum in another cycle. First, the coke drum is steam purged and cooled with quench water. The coke drum is then drained of water and vented to atmospheric pressure, after which the top and bottom flanges are removed. Removing the top and bottom flanges effectively functions to de-head the coke drum. Stated another way, removal of the flanges effectively removes the coke head that formed during the manufacturing process that is adjacent the flanges. Once the coke drum is de-headed, the coke remaining within the coke drum is removed (typically by water cutting the coke from the drum) and emptied into a catch basin, typically a rail car. Once the coke is removed, the heads are replaced and the coke drum is prepared to repeat the cycle.
This process of unheading or de-heading the coke drum can be extremely dangerous for several reasons. To mention only a few, the cooling water introduced into the hot drums prior to the removal of the bottom flange becomes extremely hot and could leak from the loosened flange and scald surrounding operators, the load of un-drained water and loose coke within the drum may exceed the limits of the support system and cause heavy equipment to fall, positioning the chute and necessary removal of the flanges or heads is done with operators who are in close proximity to the drums, loose coke within the coke drum may fall and injure workers as the flanges are removed, and operating personnel may be exposed to finely divided coke particles, steam, hot water and noxious gases, when the drum is opened. Unfortunately, several accidents and even some fatalities occur each year as a result of the de-heading process used during this particular type of manufacturing process.
Prior art systems and methods have tried to more efficiently and effectively de-head coke drums, as well as to minimize many of the dangers inherent in the de-heading process. One such method involves placing a de-heading cart under the drum, raising a flange support ram, with braces installed, and loosening some (up to one half) of the flange bolts by manual operation with an impact wrench. Following the water quench and drain, the remaining bolts are manually removed, braces are removed from the ram, the approximately 4-ton flange is lowered, and the cart, with flange resting thereon, is moved away. As is evident, this manual, hands-on process is extremely dangerous and has resulted in several accidents and deaths.
Other systems have been disclosed, which somewhat reduce human or manual involvement. For example, U.S. Pat. No. 4,726,109 to Malsbury et al. and U.S. Pat. No. 4,960,358 to DiGiacomo et al. describe a remote unheading device for coking drums. The device includes a head unit for attachment to a lower flange of a coking drum and a plurality of swing bolts which are disconnected by remotely operated de-tensioning equipment. A platform device lowers the head unit, moves it laterally to one side and tips it for cleaning. A chute attached to the frame can be raised into engagement with the coking drum lower flange for removal of coke from the drum.
U.S. Pat. No. 5,098,524 to Antalfy et al. filed on Dec. 10, 1990 discloses a coke drum unheading device having a pivoting actuator system operable from a location remote from a drum outlet. The actuator is adapted to move a drum head between closed and open positions and to retain the drum head in a closed position under a load.
U.S. Pat. No. 5,500,094 to Fruchtbaum provides a coke drum unheading device that retracts and tilts the bottom head incrementally so that falling debris such as shot coke can be caught by a chute. Following disposal of the loose debris, the head can be withdrawn from the area of the drum for maintenance. Specifically, the invention provides an unheading device for removing a bottom head from a flange on a lower end of a coke drum. An unheading car is horizontally movable into and from position below the bottom head. A vertically adjustable bottom head support member is mounted on the car. A bearing plate is pivotally mounted at an upper end of the support member for engaging a lower surface of the bottom head. A retractable arm has first and second sections hingedly connected at one end and having respective opposite ends secured to the bearing plate and the support member for pivoting the bearing plate and bottom head supported thereon with respect to horizontal, preferably to tilt the head towards an adjacent chute.
U.S. Pat. No. 5,581,864 to Rabet discloses an apparatus and method enabling removal of the drum head of a coke drum, which comprises an apparatus remotely placing a carriage under the drum head and the carriage is adapted to remotely engage the drum head, tightly support the head against the drum while workers are in the area, and to lower the head and carry it away. A safety feature is also included and disclosed, wherein the carriage is normally supported by springs which, in the event of excessive loads, automatically transfer the load carrier to an overhead beam designed to carry any excessive loads.
Each of these prior art devices share common deficiencies in that they are incapable of providing simple, efficient, and safe solutions to the de-heading of a coke drum. Specifically, each of the assemblies or devices require that the head or flange unit be completely removed from the adjacent or matching flange portion of the coke drum after each coking cycle and prior to the purging of the coke from the coke drum. This creates an extreme hazard to workers and provides an inefficient and time consuming procedure. In addition, the requirement to remove the flange or head unit increases the chance for accident, while at the same time increases human involvement as the head unit must be properly secured to the coke drum each operating cycle, despite the automation involved. Still, a large amount of floor space is required to accommodate those assemblies and devices that automate the removal and lifting of the flange or head unit from the coke drum.
Presently, one of the primary roadblocks to the total automation concept is the systems and methods currently employed for de-heading a coke drum or similar vessel. Whether coke drum de-heading is done entirely manually, or by any one of the above discussed prior art limited automation or semi-automated systems and devices that are currently available, there is still a significant physical human on component required in the process, primarily due to the systems and methods utilized.